So far there are 170 million diabetes patients all over the world, and most of them are Diabetes II patients (i.e., non-insulin-dependent type). Now the anti-diabetes medicines for clinical use mainly include Metformins, sulfonylureas, insulins, thiazolidinediones, α-glucosidase inhibitors and dipeptidyl peptidase-IV inhibitors. Although these medicines are effective in treatments, there exists safety concern for long term treatment, e.g., hepatotoxicity, and some of them will cause many problems such as weight gain.
Sodium glucose cotransporter 2 (SGLT2) has been discovered to be a new target for treating diabetes in recent years. SGLT2 is mainly distributed in renal proximal tubules, and serves to absorb the glucose in urine and return it back to blood. So, inhibiting SGLT2 can result in decreased glucose concentration in blood, which decreases blood glucose level by a pathway different from previous ones. More glucose will be secreted into urine when the function of SGLT2 is inhibited, which helps diabetes patients to keep normal blood glucose level. Since SGLT2 inhibitors are not involved in glucose metabolism, they may serve as a supplementary means of dominant methods for controlling blood glucose.
Chinese patent application No. CN200610093189.9 discloses a compound with the following structure as a SGLT2 inhibitor:

wherein A is O, S, NH, (CH2)n, wherein n=0 to 3.
Chinese patent application No. CN200380110040.1 discloses a compound with the following structure as a SGLT2 inhibitor:

wherein A is a covalent bond, O, S, NH, (CH2)n, wherein n=1 to 3.
Chinese patent application No. CN200480006761.2 discloses a compound with the following structure as a SGLT2 inhibitor:

wherein X is a covalent bond or a lower alkylene group.
WO 2005/012326 discloses a compound with the following structure as a SGLT2 inhibitor:
